U.S. patent application number 10/878741 was filed with the patent office on 2005-01-06 for fuse, battery pack using the fuse, and method of manufacturing the fuse.
Invention is credited to Izaki, Masatoshi, Mukai, Takahiro, Sakamoto, Yoshio, Senda, Kenji.
Application Number | 20050001710 10/878741 |
Document ID | / |
Family ID | 33549781 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050001710 |
Kind Code |
A1 |
Mukai, Takahiro ; et
al. |
January 6, 2005 |
Fuse, battery pack using the fuse, and method of manufacturing the
fuse
Abstract
A fuse has a pair of lead terminals disposed on a substrate, an
intermediate layers for welding formed on the surface of at least
one of the lead terminals, and a fuse element. The fuse element is
welded to the pair of lead terminals through the intermediate layer
so as to span the same. Further, the intermediate layer is formed
on at least one of the lead terminals except a face thereof
opposing each other. Owing to this configuration, after the fuse
has melted down, the melted fuse element is prevented from being
spread out into the space between the opposing faces of the lead
terminals and insulation therebetween is secured.
Inventors: |
Mukai, Takahiro; (Miyazaki,
JP) ; Izaki, Masatoshi; (Miyazaki, JP) ;
Sakamoto, Yoshio; (Miyazaki, JP) ; Senda, Kenji;
(Fuki, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
33549781 |
Appl. No.: |
10/878741 |
Filed: |
June 29, 2004 |
Current U.S.
Class: |
337/297 |
Current CPC
Class: |
H01H 2085/025 20130101;
Y02E 60/10 20130101; H01M 50/572 20210101; H01H 85/143 20130101;
H01H 37/761 20130101; H01M 50/581 20210101 |
Class at
Publication: |
337/297 |
International
Class: |
H01H 085/00; H01H
085/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 1, 2003 |
JP |
2003-189354 |
Claims
What is claim is:
1. A fuse comprising: a substrate; a pair of lead terminals
disposed on the substrate; an intermediate layer for welding formed
on a surface of at least one of the lead terminals except a portion
of a face where the pair of lead terminals opposing each other; and
a fuse element made of a fusible member and welded to the pair of
lead terminals through the intermediate layer so as to span the
pair of lead terminals.
2. The fuse according to claim 1, wherein the intermediate layer
includes a plated layer.
3. The fuse according to claim 2, wherein the intermediate layers
further includes a meltable layer for welding disposed on the
plated layer.
4. The fuse according to claim 1, wherein the intermediate layer is
formed at portion set back a predetermined distance from the face
where the lead terminals opposing each other.
5. The fuse according to claim 1, wherein at least one of lead
terminals has a protruded portion formed on a end portion where the
lead terminals opposing each other.
6. The fuse according to claim 5, wherein the protruded portion
prevents the intermediate layer from being formed on the face where
the lead terminals opposing each other.
7. The fuse according to claim 5, wherein the protruded portion is
edge burr present on the end portion of at least one of the lead
terminals.
8. The fuse according to claim 5, wherein the protruded portion is
a raised portion present at the end portion of at least one of the
lead terminals and having a curved surface.
9. The fuse according to claim 5, wherein the protruded portion is
formed on a cut face of the end portion of at least one of the lead
terminals.
10. The fuse according to claim 1, further comprising a cover film
for covering the fuse element.
11. The fuse according to claim 10, further comprising flux
containing rosin as a main component and sealed in the cover
film.
12. The fuse according to claim 1, wherein the fuse is at least one
of a temperature fuse and a current fuse.
13. A pack battery comprising: a battery; a body housing the
battery; a wiring led out from the body and electrically connected
to the battery; and a fuse including: a substrate; a pair of lead
terminals disposed on the substrate; an intermediate layer for
welding formed on a surface of at least one of the lead terminals
except a portion of a face where the pair of lead terminals
opposing each other; and a fuse element made of a fusible member
and welded to the pair of lead terminals through the intermediate
layer so as to span the pair of lead terminals.
14. The pack battery according to claim 13, wherein the fuse is in
contact with the body.
15. The pack battery according to claim 13, wherein the fuse is in
contact with the battery.
16. A method of manufacturing a fuse comprising the steps of: A)
bonding a pair of lead terminals on a substrate; B) forming an
intermediate layer for welding on a surface of at least one of a
pair of lead terminals except portions of faces where the lead
terminals opposing each other; and C) welding the fuse element to
the intermediate layer.
17. The method of manufacturing a fuse according to claim 16,
wherein step B comprises the steps of D) forming a plated layer on
one of the lead terminals except faces where the lead terminals
opposing each other; and E) forming a meltable layer for welding on
top face of the plated layer, wherein the fuse element is welded to
the meltable layer for welding at step C.
18. The method of manufacturing a fuse element according to claim
16, further comprising the step of: F) producing the pair of lead
terminals by cutting work and providing a protrusion on end portion
where the lead terminals opposing each other.
Description
TECHNICAL FIELD
[0001] The present invention relates to a fuse used for preventing
failure of electronic equipment and the like due to abnormal
heating and overcurrent, a battery pack using the fuse, and a
method of manufacturing the fuse.
BACKGROUND ART
[0002] In order to prevent occurrence of a failure of electronic
equipment due to abnormal heating of a pack battery used in
electronic equipment such as mobile telephones, it is required that
a temperature fuse be mounted on the pack battery. It is also
required that a current fuse be mounted on electronic equipment to
prevent occurrence of a failure due to abnormal current.
[0003] In a conventional temperature fuse, a fuse element which
melts down when it reaches a predetermined temperature is provided
at its both ends with terminal portions and the terminal portions
are connected to a circuit such as a power supplying circuit. When
abnormal heating is produced in a component constituting a power
supply or the like (such as a battery), the fuse element serves its
function at a high temperature caused by the abnormal heating.
Thus, the temperature fuse is adapted to break the circuit to
prevent the internal components and the like from being
damaged.
[0004] In the conventional fuse, a fuse element made of a fusible
member is welded to a pair of lead terminals so as to span the
same, and thereby, it is electrically connected to the lead
terminals. Fuses of the described type are disclosed in, for
example, Japanese Unexamined Patent Publication No. H11-273520 and
Japanese Unexamined Patent Publication No. 2002-33035. In those
cases, an intermediate layer for welding is provided between the
fuse element and the lead terminal for ensuring good welding of the
fuse element to the lead terminal.
[0005] FIG. 11 is a lateral sectional view of a prior art fuse.
FIG. 12 is a lateral sectional view of fuse element 104 as have
been melted down. The fuse is constructed by disposing a pair of
lead terminals 100 on substrate 103 and by welding fuse element 104
to lead terminals 100 through plated layer 101 provided on the
surface of lead terminals 100. Though it is not shown, some flux or
a cover may be provided on fuse element 104. A fuse is manufactured
in the following way. First, a pair of lead terminals 100 are
disposed on substrate 103. Then, plated layers 101 are formed on
the pair of lead terminals 100 arranged as above. At this time,
plated layers 101 are formed so far as they are even spread on
opposing faces 102 of lead terminals 100. Fuse element 104 is
placed on plated layers 101 and pressed and heated from its upper
side to be welded to plated layers 101. A fuse is manufactured
through the above described steps.
[0006] However, in the prior art fuse, plated layers 101 are formed
to be extended over opposing faces 102. Therefore, when fuse
element 104 is welded, spread-out portions 105 thereof are formed
on the opposing portions so that the insulation distance between
lead terminals 100 opposing each other is shortened. Furthermore,
when fuse element 104 is melted down, melted fuse element 104 is
spread out over opposing faces 102, whereby large spread-out
portions 105 are formed as shown in FIG. 12. Then, the insulation
distance between opposing lead terminals 100 becomes still shorter
after the melting down of the fuse element. Hence, insulating
capability becomes insufficient though the fuse element is melted
down.
[0007] In a case of a large sized fuse, it is no problem if there
exist spread-out portions 105 because lead terminals 100 originally
have a large face-to-face distance. However, in these days,
electronic equipment is becoming increasingly smaller in size and
lower in profile. Also with respect to batteries having fuses
mounted thereon, advances are being made in making them lower
profiled and smaller sized. This makes it indispensable to make the
fuse smaller sized and lower profiled and it is naturally required
to narrower the face-to-face distance of lead terminals 100.
However, there is a limit in making the face-to-face distance
narrower due to the deterioration of insulating capability caused
by existence of spread-out portions 105. Hence, it is required to
previously provide a sufficiently large face-to-face distance. As a
result, it becomes impossible to make the fuse smaller sized and
lower profiled.
SUMMARY OF THE INVENTION
[0008] A fuse of the present invention has a substrate, a pair of
lead terminals disposed on the substrate, an intermediate layer for
welding formed on the surface of at least one of the lead
terminals, and a fuse element made of a fusible member. The fuse
element is welded to the pair of lead terminals through the
intermediate layer such that is spans the pair of lead terminals.
The intermediate layer is formed on at least one of the lead
terminals except a face thereof opposing each other. Further, a
method of manufacturing a fuse of the present invention includes a
step of connecting a pair of lead terminals onto a substrate, a
step of forming an intermediate layer for welding on the surface of
at least one of the lead terminals except a face of thereof
opposing each other, and a step of welding the fuse element to the
intermediate layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a lateral sectional view of a fuse in an
embodiment of the present invention.
[0010] FIG. 2A is a lateral sectional view of a lead terminal in
the fuse shown in FIG. 1.
[0011] FIG. 2B is a lateral sectional view of another lead terminal
in an embodiment of the present invention.
[0012] FIG. 3-FIG. 7 are drawings showing steps in manufacturing of
the fuse shown in FIG. 1.
[0013] FIG. 8A-FIG. 8C are drawings showing steps in welding of a
fuse element of the fuse shown in FIG. 1.
[0014] FIG. 9 is a perspective view showing the fuse of FIG. 1 with
its fuse element melted down.
[0015] FIG. 10A and FIG. 10B are perspective views with a portion
broken away of a pack battery according to an embodiment of the
present invention.
[0016] FIG. 11 is a lateral sectional view of a conventional
fuse.
[0017] FIG. 12 is a lateral sectional view of the conventional fuse
with its fuse element melted down.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0018] An exemplary embodiment of the present invention will be
described with reference to the accompanying drawings. A case where
a single structure of a plated layer is used for the intermediate
layer for welding, or a case where a combined structure of a plated
layer and a meltable layer for welding is used therefor, will be
taken as an example in the following description.
[0019] FIG. 1 is a lateral sectional view of a fuse in the first
exemplary embodiment of the present embodiment. FIG. 2A and FIG. 2B
are lateral sectional views of lead terminals. FIG. 3 to FIG. 7 are
drawings showing steps in manufacturing the fuse and FIG. 8A to
FIG. 8C are drawings showing steps in welding the fuse element.
FIG. 9 is a perspective view of a fuse melted down.
[0020] Substrate 1 is made of an insulating material, such as a
plastic, glass, or ceramic material, or it may be made of metal
with an insulating coating formed thereon. In the present
embodiment, an alumina ceramic plate is used as substrate 1.
Substrate 1 may be formed not only of a rectangular plate but also
of a disk, oval, triangular, pentagonal, or a polygonal plate in
polygonal number of five or larger. A pair of lead terminals 2 are
bonded onto substrate 1 and arranged to oppose each other. Lead
terminals 2 are made of an electrically conductive material and
preferably made of metal. To be concrete, a single metallic
material, at least, selected from iron, nickel, copper, aluminum,
gold, silver, and tin, or an alloy made of the metallic materials
may be used. Otherwise, a metallic material and the like obtained
by adding an element or elements not belonging to the above
material group to a single material, at least, selected from the
above material group or an alloy may be used.
[0021] As the material for bonding lead terminal 2 onto substrate
1, a plastic resin, glass, or a metallic film containing a plastic
resin or glass may be used. When a metallic film is used as a
bonding agent, the metallic film is formed on substrate 1 by
printing or the like, lead terminals 2 are placed on the metallic
film, and lead terminals 2 are bonded to substrate 1 by such a
method as ultrasonic welding. When the material of substrate 1 is a
thermoplastic resin, such a method may also be used as to place
lead terminals 2 on substrate 1 and then apply quick heating,
followed by quick cooling, to them to have the surface of substrate
1 directly melted. In the present embodiment, a nickel plate with
its surface plated with tin is used as lead terminal 2 and an epoxy
resin containing filler formed of alumina and silica is used as the
bonding agent.
[0022] A pair of lead terminals 2 are arranged to have their
opposing faces 5 opposing each other across face-to-face distance
31. When a fuse is made small in size, distance 31 must be reduced
correspondingly. It is an important factor how to reduce distance
31 in realizing a small-sized fuse. When distance 31 is extremely
small, a sufficient insulating capability cannot be provided
between lead terminals 2 after melting down of fuse element 4.
Accordingly, distance 31 needs to be large enough to secure the
insulating capability.
[0023] Plated layers 3 are formed on the surfaces of lead terminals
2. At this time, plated layers 3 are formed on the surfaces except,
at least, opposing faces 5. Further, there are provided non-plated
regions 6 in the ranges of a predetermined distance from the end
faces of lead terminals 2 opposing each other. In other words,
plated layers 3 are formed at the portions a predetermined distance
set back from the end faces of lead terminals 2 opposing each
other. By virtue of the existence of non-plated regions 6,
formation of spread-out portions of fuse element 4 is prevented
more positively as discussed in the following. As the material of
plated layer 3, is used such a metallic material as tin, copper,
silver, gold, nickel, and zinc. If formation of plated layers 3 is
confined to the surfaces of the end portions of lead terminals 2
except, at least, opposing faces 5 opposing each other, it may be
unnecessary to provide non-plated regions 6. Further, non-plated
regions 6 may be provided by small amounts of edge burrs 12
produced at the cut faces of end portions 51 of lead terminals 2.
Namely, as shown in FIG. 2A, a small amount of non-plated region 6
with width 32 may be secured by edge burr 12. Further, edge burrs
12 are protruded portions provided at end portions 51 of lead
terminals 2 opposing each other and they are raised portions having
curved surfaces 121. Edge burr 12 also serves for preventing plated
layer 3 from being formed on opposing face 5.
[0024] Instead of providing plated layer 3, a metal paste such as a
silver paste may be applied. Otherwise, metal depositing or
sputtering may be applicable. Plating may be either electroplating
or electroless plating, or an electroplated layer may be formed on
an electroless plated layer. Further, plated layer 3 may be formed
of a single layer or plural, two or more, layers. By forming plated
layer 3 in plural layers, a merit can be obtained that weldability
with fuse element 4 is enhanced and the strength of weld is
secured. Further, it is preferable to select materials having good
welding compatibility with the material of fuse element 4.
[0025] Fuse element 4 is a fusible member, which is welded onto
plated layers 3 and electrically connected with lead terminals 2
through plated layers 3. Fuse element 4 is welded to lead terminals
2 at end portions thereof opposing each other and so connected as
to span the pair of lead terminals 2. Fuse element 4 is a material
to produce a fusing function. As current fuses, such material may
be used as gold, copper, silver, nickel, aluminum, tin, and a
compound or alloy of such materials. As temperature fuses, such
low-melting point metal as tin, bismuth, indium, lead, and cadmium
may be used as a single metal or an alloy having such metals mixed
therein. In the present embodiment, a fuse element of a temperature
fuse formed of a ternary alloy of tin, bismuth, and lead and having
a melting point of 96.degree. C. is used as fuse element 4.
Although fuse element 4 used in the present embodiment is
substantially rectangular parallelepiped, that in a disk shape,
cylindrical shape, or linear shape may be used.
[0026] Although it is not shown in FIG. 1 and FIG. 2A, fuse element
4 may be welded onto the surfaces of plated layers 3 after applying
a welding flux to the surfaces. The welding flux is an auxiliary
agent for electrically connecting fuse element 4 with lead
terminals 2 and it is selected after making it sure that its
compatibility with the material of lead terminals 2 and the
material of fuse element 4 is good. For example, a liquid flux of
the rosin group may be selected as the welding flux.
[0027] In addition to the above mentioned components, cover film 27
may be provided to cover the fuse portion including fuse element 4
as shown in FIG. 1. This arrangement is meritorious because melted
fuse element 4 is thereby prevented from spattering around.
Further, cover film 27 may be formed of an upper and a lower film
pasted together or may be formed of a single sheet of film rolled
up. Further, flux 28 containing rosin and the like to facilitate
melting down of fuse element 4 may be filled in the interior of
cover film 27. This also prevents melted fuse element 4 from
spattering around.
[0028] Further, fuse element 4 may be welded onto plated layer 3
after disposing meltable layer 13 for welding thereon as shown in
FIG. 2B. Namely, the intermediate layer for welding may be formed
of two layers of plated layer 3 and meltable layer 13. Thereby,
such a merit can be obtained that the strength of connection
between fuse element 4 and lead terminals 2 is enhanced. As
meltable layer 13, a meltable metal such as a solder and silver
paste is suitable.
[0029] With reference to FIG. 3 to FIG. 8C, steps in manufacturing
process of a fuse will be described below. FIG. 3 shows step 1,
FIG. 4 step 2, FIG. 5 step 3, FIG. 6 step 4, and FIG. 7 shows step
5.
[0030] First, at step 1, substrate 1 is prepared. Then, at step 2,
a pair of lead terminals 2 are bonded onto substrate 1. They are
bonded via thermo-compression bonding, or a solvent including
adhesive components is used for bonding. At this time, face-to-face
distance 31 of lead terminals 2 is set so large that insulating
capability between lead terminals 2 after melting down of fuse
element 4 as described above can be secured. A metal ribbon or the
like are cut to produce lead terminals 2. Then, edge burrs
(protrusions) 12 are sometimes produced at end portions 51 of lead
terminals 2 opposing each other as shown in FIG. 2A. Edge burrs 12,
as described in the foregoing, serve as non-plated regions at step
3 that follows.
[0031] At subsequent step 3, plated layers 3 are formed on portions
of the surfaces of lead terminals 2. At this time, plated layers 3
are formed on the portions of lead terminals 2 except opposing
faces 5. When required, plated layers 3 are formed except
non-plated regions 6 provided in ranges a predetermined distance
set back from the opposing end faces of lead terminals 2. To
achieve this, plating may be performed on lead terminals 2 after,
for example, masking non-plated regions 6 and opposing faces 5 with
a resin film or the like, and the resin film may be peeled off
after plating. Otherwise, edge burrs 12 unavoidably formed by
cutting work as described above may be positively utilized for
preventing plated layers 3 from being formed on opposing faces 5.
Further, when necessary, meltable layers 13 may be formed at least
at a portion of the top face of plated layers 3 as shown in FIG.
2B. In that case, fuse element 4 is welded to meltable layers 13 at
below discussed step 5. Further, when it is needed, a flux mainly
composed of rosin may be placed on the surface of plated layers
3.
[0032] Then, at step 4, fuse element 4 formed of a fusible member
is placed on lead terminals 2. Fuse element 4 here is in a
parallelepiped shape. Due to placing fuse element 4 such that its
end face comes within the range of the top face of plated layers 3,
the welding to be described at step 5 becomes easy. Fuse element 4
may otherwise be placed beyond the range of plated layer 3.
[0033] Then, at step 5, fuse element 4 is welded onto plated layers
3. Due to being welded to plated layers 3, fuse element 4 is
electrically connected to lead terminals 2 and enabled to function
as a fuse. Weld portion 7 ensures connection of fuse element 4 to
plated layer 3. According to need, fuse element 4 may be filled in
cover film 27 or a case, or flux 28 may be applied to it. Fuse
element 4 may be in an oval or linear form other than the
rectangular parallelepiped form.
[0034] At steps 1 and 2, such processes are described in which
plated layers 3 are formed on lead terminals 2 after lead terminals
2 have been bonded to substrate 1. Other than that, lead terminals
2 having been provided with plated layer 3 may be bonded to
substrate 1. Otherwise, fuse element 4 may be welded to lead
terminals 2 having been provided with plated layers 3 and,
thereafter, lead terminals 2 may be bonded to substrate 1. Such
processes may be suitably changed according to incurring cost and
ease of processing.
[0035] Welding of fuse element 4 will now be described in detail
with reference to FIG. 8A-FIG. 8C.
[0036] First, cooling plate 8 is placed, as shown in FIG. 8B, on
the top face of fuse element 4 mounted on lead terminals 2 so as to
span the same as shown in FIG. 8A. Cooling plate 8 has an effect to
temporarily fix fuse element 4 onto lead terminals 2 mechanically
and another effect to cool fuse element 4. As the material of
cooling plate 8 to obtain a cooling effect, a material having a
thermal conductivity of at least 20W.multidot.m.sup.-1K.sup.-1 may
be used. To be concrete, aluminum, magnesium, copper, titan, gold,
silver, nickel, iron, carbon (graphite), and silicon may be used as
a single metal, as an alloy of such metals, as an oxide or nitride,
or a composite of them. In the case of the present embodiment, an
aluminum alloy including at least 90% of aluminum is used.
[0037] There is glass as a material having thermal conductivity
lower than 20W.multidot.m.sup.-1K.sup.-1, namely 1.1
W.multidot.m.sup.-1 K.sup.-1. If such a material is used for
cooling plate 8, the effect to temporarily fix fuse element 4 to
lead terminals 2 mechanically can be obtained. However, at the time
of welding of fuse element 4, fuse element 4 is spheroidized near
the weld portion by the melting heat at the weld portion.
Otherwise, there is formed a narrowed or broken portion between the
center of fuse element 4 and the weld portion or an unwelded
portion when the welding heat is low. Therefore, limits are imposed
on welding conditions and the production yield is lowered in the
case of mass production.
[0038] Then, end portions 4A, 4B of fuse element 4 are heated to be
welded to plated layers 3. There are various ways for heating end
portions 4A, 4B of fuse element 4. Such methods are possible as to
heat lead terminals 2 with heaters, to pass a current through lead
terminal 2 alone so that lead terminal 2 proper is heated to a high
temperature, and to heat lead terminal 2, end portion 4A and end
portion 4B directly with infrared rays. In the present embodiment,
laser beams 9 of near-infrared regions are radiated in the
direction indicated by the arrows. Thereby, plated layers 3 and
fuse element 4 are welded together.
[0039] Then, cooling plate 8 is removed from the fuse element 4
after the welding as shown in FIG. 8C. Since fuse element 4 is
melted only at end portions 4A, 4B, and scarcely melted at the
portion kept in touch with cooling plate 8 during the welding, the
cross-sectional configuration of fuse element 4 is kept. Therefore,
the welding conditions are not so much limited and variations in
resistance value are kept low even if the fuses are mass-produced
and, hence, production yield is greatly improved.
[0040] In order to enhance the cooling effect of cooling plate 8,
it is effective to place a liquid having a boiling point close to
the melting point of fuse element 4 between cooling plate 8 and
fuse element 4. Then, the cooling effect is enhanced by
vaporization heat of the liquid. Further, due to the liquid filled
in a small gap between cooling plate 8 and fuse element 4, the
effect of heat conduction to the cooling plate 8 is enhanced.
Further, by the liquid washing out dirt on cooling plate 8 due to
repeated use of it, foreign substances are prevented from attaching
to cooling plate 8. To be concrete, pure water, methanol, ethanol,
propanol, and butanol may be used. A solvent used in a liquid flux
is preferably used.
[0041] Through the above steps of processing, fuse element 4 and
plated layers 3 are welded together and thereby lead terminals 2
are electrically connected with fuse element 4.
[0042] Since, at this time, plated layers 3 are formed at the
portions excluding opposing faces 5, fuse element 4 as a fusible
member is prevented from forming spread-out portions over opposing
faces 5. Further, when plated layers 3 are formed at the portions
excepting, further, non-plated regions 6, which are set back from
the opposing faces of lead terminals 2, practically no spread-out
portions are formed. Therefore, formation of spread-out portions to
shorten the insulation distance of lead terminals 2, as is in the
case with the prior art where the plated layers were formed on the
faces including the opposing faces, can be prevented from occurring
at the time of welding of fuse element 4. Thus, the insulation
distance is prevented from being narrowed and the preset distance
31 for securing insulating capability can be maintained.
[0043] Below will be given description about melting down of fuse
element 4. Fuse element 4 is a fusible member and made of metal or
the like as a conductor. Therefore, a current flows between lead
terminals 2 through fuse element 4. When the flow of current
exceeds a predetermined value and becomes an overcurrent, fuse
element 4 generates heat greatly and exceeds its melt-down
temperature to be melted down. Likewise, when electronic equipment
or a battery pack incorporating a fuse generates heat abnormally to
raise its temperature, the fuse exceeds its melt-down temperature
to be melted down. The former is a case where the fuse is used as a
current fuse and the latter is a case where the fuse is used as a
temperature fuse.
[0044] FIG. 9 shows a fuse as have been melted down. Incidentally,
there are not shown cover film 27 and flux 28 in FIG. 9. When fuse
element 4 melts down upon exceeding its melt-down temperature, fuse
element 4 is torn apart at melted portion 10 toward the sides of
both lead terminals 2 so as to collect on the upper surfaces of
plated layers 3. As a result, melted-down fusible member 11
coagulates on each of the top faces of two plated layers 3. Hence,
melted-down fusible members 11 produced by melting down of fuse
element 4 are prevented from being spread out into the space
between the opposing sides of lead terminals 2. Namely, melted-down
fusible members 11, even after being melted down, are not spread
out into the space between lead terminals 2 and, hence, the
insulation distance is not narrowed. Therefore, the insulation
distance is maintained as preset face-to-face distance 31 after the
melting down, and hence insulating capability can be fully
maintained. In the case of the prior art where plated layers 101
are disposed as far as they reach opposing faces 102, melted fuse
element 104 is spread out over plated layers 101 and, thereby, the
insulation distance is decreased corresponding to the spread-out
amount. In this case, although the face-to-face distance is
determined at the stage of designing to secure required insulating
capability, the insulation distance after the melting down becomes
shorter than the designed face-to-face distance and there arises
the possibility that the designed insulating capability becomes
unobtainable. If, allowing for it, the face-to-face distance is set
larger at the time of designing, reduction in size of the fuse
cannot be attained. In the case of the fuse of the present
embodiment, in contrast with prior art fuses, spread-out portions
are not formed on opposing faces after the melting down and, hence,
insulating capability can be secured.
[0045] Therefore, in contrast to the case of melting down in the
prior art fuses, the face-to-face distance of lead terminals after
melting down, i.e., the insulation distance, can be maintained the
same as face-to-face distance 31 set at the time of designing.
Hence, a fuse can be constructed with a smaller
terminal-to-terminal distance. As a result, a fuse smaller in size
than that in the prior art can be realized and, also, by the use of
the fuse, it becomes possible to configure a temperature fuse and
current fuse very small in size.
[0046] Now will be described an example in which the fuse
configured as above is applied to a battery pack, hereinafter. FIG.
10A, FIG. 10B are perspective views with a portion broken away of a
battery pack according to the present embodiment of the
invention.
[0047] Fuse 22 is a fuse of the above described configuration and
it is used as a temperature fuse. In fuse 22, a pair of lead
terminals 24, 25 are bonded to the top of a substrate and a fuse
element made of a fusible member is welded to lead terminals 24, 25
so as to span the same. The fuse element is welded to lead
terminals 24, 25 through the plated layers which are formed thereon
except opposing faces of the lead terminals. Hence, the fuse
element even after it has been melted down is prevented from being
spread out over the opposing faces of the lead terminals. Further,
a center of fuse 22 is covered with a cover film made of PEN
(polyethylene naphthalate) and a flux containing rosin and the like
as the main components is sealed therein.
[0048] Wiring 23A is led out from either positive or negative
terminal 26 of battery 20. One lead terminal 24 of fuse 22 is
connected with wiring 23A led out from battery 20, while the other
lead terminal 25, is connected with wiring 23B across fuse 22.
Wiring 23B is led out of the outside of casing 21, constituting the
main body of pack battery 19, as a battery terminal of the same
polarity as that connected with wiring 23A (namely, a positive or
negative terminal of battery 20) and connected to another
electronic component (not shown) to realize power supply. The
terminal of opposite polarity of battery 20 is led out separately
and connected to the electronic component. Thereby, power is
supplied from pack battery 19 to the electronic component. Namely,
fuse 22 is attached to either positive or negative terminal 26 of
pack battery 19 and disposed between wirings 23A, 23B.
[0049] When abnormal heat is produced in pack battery 19, the fuse
element made of a fusible member is melted down and fuse 22 is
rendered non-conductive. Hence, power supply from pack battery 19
is cut off. By the cutoff of the power supply, heat production
thereafter is suppressed and occurrence of damage to the user due
to the abnormal heat can be prevented. Further, even when the
current value becomes abnormally large, the fuse element melts down
due to heat produced by the overcurrent, whereby fuse 22 is
rendered non-conductive. Thereby, influence to the user and failure
of the electronic equipment caused by overcurrent thereafter can be
prevented.
[0050] At this time, even after the melting down, the melted fuse
element is prevented from being spread out over the opposing faces
of lead terminals 24, 25 as described above. Accordingly, such a
problem does not arise that the insulation distance becomes shorter
after the melting down and a proper insulating capability is made
unobtainable. With prior art fuses, there are cases where objects
to be attained by the fuses, i.e., protection of electronic
equipment and users from abnormal heating and overcurrent, are
unattainable, though the fuse has been melted down, because of the
formation of the spread-out portions and, hence, sufficient
insulation is not secured. In contrast therewith, in the case of
fuses of the present embodiment, the insulation distance is not
shortened and maintained as the preset face-to-face distance after
the melting down, and hence the insulating capability is maintained
as originally designed. Therefore, electronic equipment and users
are protected by the melting down from abnormal temperature or over
current. Further, since the insulation distance is not shortened by
the melting down, it is possible to design originally the distance
between the lead terminals at the minimum value capable of securing
sufficient insulation. Thus, it is made possible to produce fuse 22
in small size. Therefore, even if pack battery 19 is made smaller
sized and lower profiled, a fuse can be mounted thereon and, hence,
it is made possible to provide a fuse capable of keeping pace with
the development of miniaturization of pack battery 19.
[0051] An example where fuse 22 is mounted on pack battery 19 is
shown in FIG. 10A. Otherwise, the fuse can function as a current
fuse even if it is mounted on an electronic substrate or around an
IC.
[0052] Further, pack battery 19 is mounted on a mobile telephone,
personal digital assistance, notebook-size computer, and the like.
The same may be said, not only of the battery mounted on such
electronic apparatuses as mentioned above, but also of the battery
mounted on a desktop personal computer and precision electronic
instrument. In order that such electronic apparatuses are protected
from abnormal heat and over-current and that users are prevented
from suffering damage before it occurs, mounting of a fuse on them
is important. In this connection, while a large number of pieces of
electronic equipment are being made smaller sized, lower profiled,
and more densely packed, miniaturization of fuses mounted on them
becomes important. Under these circumstances, since the insulation
distance of the lead terminals after the fuse has melted down and
the face-to-face distance of the lead terminals designed for
securing insulation can be made identical, very small fuses can be
realized. Therefore, it becomes possible to meet requirements for
the electronic equipment incorporating the fuses.
[0053] Although fuse 22 is disposed so as to contact with casing 21
forming the body of pack battery 19 in FIG. 10A, it may be disposed
in contact with battery 20 as shown in FIG. 10B to operate more
accurately as a temperature fuse.
[0054] Although the intermediate layers including plated layers 3
or meltable layers 13 are provided on a pair of lead terminals 2 in
the present embodiment, the intermediate layer may be provided on
only one of lead terminals 2. This structure has an effect like
that including intermediate layers on both lead terminals 2 as
described above. Edge burrs (protrusions) 12 or protruded portions
having curved surfaces 121 may be provided on only one of lead
terminals 2.
[0055] In the present invention, intermediate layers for welding
used in the welding of a fuse element to lead terminals are formed
on the lead terminals except opposing faces of the lead terminals.
Thereby, formation of spread-out portions over the opposing faces
of the lead terminals is prevented from occurring when the fuse
element is welded, and hence the insulation distance is prevented
from being narrowed. Further, when the fuse element has been melted
down, the melted fuse element is prevented from being spread out
over the opposing faces. Hence even after the melting down, the
insulation distance remains intact and the insulating capability is
secured. Therefore, the face-to-face distance of the lead terminals
set at designing can be made equal to the distance required for
securing the insulating capability. Accordingly, the face-to-face
distance can be originally set to a minimum possible value and it
is made possible to realize small sized and low profiled fuses.
Further, it is made possible to realize miniaturization of pack
batteries with a fuse mounted thereon and electronic equipment
incorporating such a battery.
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